U.S. patent application Ser. No. 336,001, filed Apr. 10, 1989, discloses, among other things, polyurethane structural adhesive compositions, and polyurethane base resins used in forming such compositions. This U.S. patent application Ser. No. 336,001 discloses that the polyurethane base resins are prepared by reacting a stoichiometric excess of polyisocyanate compound with at least one polyol compound. The stoichiometric excess of polyisocyanate compound produces isocyanate terminals on the reaction product that can be reacted further with species containing at least two active hydrogen atoms, such as primary and secondary polyamines, water, polyalcohols, polyacids and polymercaptans, resulting in curing.
Various exemplary suitable polyisocyanate compounds useful for preparing the polyurethane base resin are disclosed in U.S. patent application Ser. No. 336,001, such compounds generally being disclosed as including aromatic, aliphatic, cycloaliphatic and aralkyl polyisocyanate compounds containing from about 6 to about 100 carbon atoms. A number of specific polyisocyanate compounds are disclosed, and it is disclosed that 4, 4'-diphenylmethane diisocyanate (MDI) is preferred for preparing the polyurethane base resin.
This U.S. patent application Ser. No. 336,001 also discloses various polyols suitable for use in preparing the polyurethane base resin; e.g., U.S. patent application Ser. No. 336,001 discloses that saturated copolyester diols are most preferred because by using combinations of various types of such diols the final adhesive properties can be adjusted to achieve desired properties. U.S. patent application Ser. No. 336,001 also discloses that ring-opened polymers of cyclic esters, such as polycaprolactone, can also be used; and that the so-called polymer polyol compositions such as polyether polyols and/or polyester polyols, and also polyols which can be attained by polymerizing ethylenically unsaturated compounds in a polyether or polyester polyol, are suitable.
There is also disclosed in U.S. patent application Ser. No. 336,001 a type of polyurethane base resin most preferred for use for producing thermosetting polyurethane structural adhesive compositions disclosed in U.S. patent application Ser. No. 336,001. U.S. patent application Ser. No. 336,001 also discloses that this most preferred polyurethane base resin may be used, without modification, as a reactive adhesive composition that is cured by atmospheric moisture. U.S. patent application Ser. No. 336,001 further discloses that this most preferred polyurethane base resin is prepared by reacting a stoichiometric excess of a polyisocyanate with a combination of three different types of hydroxyl-terminated, linear, saturated copolyesters each having a molecular weight between 1000 and 6000 g/mol.
While application Ser. No. 336,001 discloses polyurethane base resins, and thermosetting polyurethane composites and thermosetting polyurethane adhesive compositions utilizing such polyurethane base resins, having improved performance characteristics over previously known materials, it is still desired to provide polyurethane base resins, and composites and compositions formed utilizing such polyurethane base resins (for example, thermosetting polyurethane adhesive compositions formed utilizing (e.g., formed by curing) such polyurethane base resins), having enhanced performance characteristics, particularly when subjected to elevated service temperatures (in particular, it is desired to provide thermosetting polyurethane adhesive compositions having enhanced performance, including improved tensile strength and adhesion at elevated temperatures).
More generally, it is desired to provide isocyanate-functional materials that are liquids or thermoplastic solids, but that are ultimately thermosetting by reaction with any typical active hydrogen-containing species that will react with isocyanates and promote curing (e.g., atmospheric moisture, or in situ water generating agents, or amine-functional solid polyamide resins), to provide a cured product having superior performance (e.g., as an adhesive) at elevated service temperatures.